Typically, films prepared for use as label facestock are coated on the printing side with a coating, which enhances ink adhesion. For instance, U.S. Pat. No. 5,380,587 to Musclow et al. discloses a multilayer packaging or label stock film having excellent printability and non-blocking characteristics. The film is first primed and then coated with copolyester coating. Another ink adhesion enhancing coating is described in U.S. Pat. No. 5,382,473 to Musclow et al. which discloses a multilayer film structure with a prime coating which is the reaction product of acidified aminoethylated vinyl polymer and epoxy resin, top coated with polyester ink base to eliminate blocking. U.S. Pat. No. 5,662,985 to Jensen et al. discloses a two-side coated label which comprises a polymeric film substrate having on a first surface thereof (A) an adhesive anchor layer and on a second surface thereof (B) an ink base layer, the (A) and (B) layers being selected from the group consisting of: (i) a prime coating having on an external surface a functional coating of an interpolymer of (a) an alpha, beta-monoethylenically unsaturated carboxylic acid; and (b) a neutral monomer ester comprising an alkyl acrylate ester and an alkyl methacrylate ester; and (ii) an iminated polymer; or the (A) adhesive anchor layer being selected from the group consisting of: (iii) a mixture of the functional coating of (i) and the iminated polymer of (ii); (iv) a linear water dissipatable polyester condensation product; and (v) a polyester; or the (B) ink base layer being selected from the group consisting of: (vi) a prime coating having on an external surface a functional coating of an acrylic copolymer; and (vii) a prime coating having on an external surface a functional coating of a styrene copolymer, provided that each of the (A) adhesive anchor layer and the (B) ink base layer is different. U.S. Pat. No. 6,025,059 to McGee et al. discloses a plastic film coated with a printable epoxy coating which is the reaction product of a water-dispersible or -soluble epoxy resin, and an acidified aminoethylated vinyl polymer produced by polymerizing acrylate or other monomer, with methacrylic or acrylic acid. The acidified aminoethylated vinyl polymer is used as a hardener or curing agent. Republic of South Africa Patent Application 970523 (UCB) discloses a printable film coated with a layer containing water dispersible polymer and polyfunctional acrylates resulting from the esterification of a polyol (rather than epoxide) with (meth)acrylic acid or polyallyl derivatives.
The development of commercially acceptable coated plastic films for printing applications, e.g., printable labels, is often a compromise between a variety of desired properties. Labels used for beverage containers, or health and beauty containers, should be capable of exposure to severe conditions encountered during manufacturing, transport and storage. Thus printable coatings for plastic films should exhibit hot water resistance, organic solvent resistance, e.g., isopropyl alcohol resistance, abrasion resistance, and haze resistance on exposure to hot or cold water. At the same time, the coating should be receptive to ink so as to provide good adhesion of the ink to the coated film immediately after printing. The ink should stay adhered to the coated film after a label is made and applied to a beverage container that is exposed to hot or cold water and subsequent abrasion encountered in mechanized handling.
Non-crosslinked polymer constituents of coatings tend to increase in haze upon exposure to boiling water and may be completely soluble and removed upon exposure to isopropyl alcohol. In addition, after ink is applied and the label exposed to water and abrasion simulating a bottling line, the ink will abrade off the label. Coatings can be made resistant to hot water or chemicals by crosslinking polymers in the coating. However, when crosslinked, coatings are generally less receptive to inks, losing the ability to have good ink adhesion immediately after printing, especially at high printing speeds and low temperature.
It would be desirable to control crosslinking of polymers to obtain desirable water and chemical resistance properties while maintaining the ink adhesion and abrasion resistance associated with non-crosslinked polymers, as well as other properties that coated plastic films for printing applications should provide, including good graphics, ink gloss and short “tack up” times.
Accordingly, it is an object of the present invention to provide printable coated plastic films that comprise cross-linkable polymers which are cross-linked to an extent sufficient to provide boiling water resistance and isopropyl alcohol resistance while maintaining desirable ink adhesion properties.